What operating system version, and do you have any backups of your data off the machine? TimeMachine? Option Key bootable clones? Storage? DVD's?
A reinstall of the operating system may be in order as a last resort, so if any of these steps on these links get you into the machine, make sure to backup your personal data (Music, Pictures, Documents, Movies) off the machine to a non-encrypted powered external drive regular storage drive (not TimeMachine as it might be corrupted too) and disconnect as soon as possible.
Good Luck and report back all what you tried.
Also report what change occured before this tragedy happened, was there a Software Update? A EFI firmware update? Etc.
To boot off the 10.6 install disk, hold c or option key while the disk is in the machine.
To boot into 10.7 Recvoery mode, hold the command and r keys down while booting.
To use Safe mode, hold down the Shift Key while booting.